Performance characteristics of snowmobiles, including the comfort of the ride, depend upon a variety of systems and components, including the snowmobile suspension. Typically, a snowmobile suspension includes two systems, a front suspension system for the skis and a rear suspension system for the track.
The rear suspension of a snowmobile supports an endless track driven by the snowmobile engine to propel the machine. The track is supported beneath the vehicle chassis by a suspension that is designed to provide a comfortable ride and to help absorb the shock of the snowmobile crossing uneven terrain. Most modern snowmobiles utilize a slide rail suspension which incorporates a pair of slide rails along with several idler wheels to support the track in its configuration. The slide rails typically are suspended beneath the chassis by a pair of suspension arms, each arm being attached at its upper end to the chassis of the snowmobile, and at its lower end to the slide rails. The mechanical linkage of the slide rails to the suspension arms and to the snowmobile chassis typically is provided with springs and one or more (often two) shock absorbers, the springs being loaded to urge the slide rails downwardly away from the snowmobile chassis, and the shocks providing dampening forces for ride comfort.
A variety of configurations of suspension arms, springs, shocks, and shock rods have been utilized to alter the characteristics and feel of the ride given by a particular suspension system. U.S. Pat. No. 5,265,692 (Mallette) shows a snowmobile track suspension having a pair of generally parallel suspension arms connecting the slide rails to the snowmobile chassis. The lower end of the rear suspension arm has a pivot mount that is movable longitudinally of the slide frame. When this pivot is located at its forward most portion of longitudinal movement (i.e., at the forward end of a longitudinal slot), the suspension arms form a parallelogram with the snowmobile chassis and the slide rails so that upward movement of the front suspension arm is transmitted through the slide rails to the rear suspension arm, causing the slide rails to move upward in an orientation that is generally parallel to the snowmobile chassis. Thus, the front end of the slide rails cannot move higher than the back end of the slide rails. The longitudinal slot into which the lower end of the rear suspension arm is pivotally mounted, however, permits the back end of these slide rails to move higher than the front end of the rails. It is said in the Mallette patent that permitting the back end of the slide rails to move upwardly produces a comfortable ride as bumps in the terrain are encountered.
Applicant has found, however, that the Mallette suspension, like many other suspensions, may seem optimized for certain conditions, but performs less optimally in other conditions. For example, in relatively deep powder, it may be particularly desirable to permit the front end of the slide rail suspension to move higher than the rear of the suspension, making it somewhat easier for the snowmobile track to plane out or rise above the powdery snow. Conversely, the amount that the back end of the slide rails are permitted to rise above the front end of the slide rails (or, to say it a different way, the amount that the snowmobile is permitted to "rock backwards" on the suspension) has an effect on the amount of weight transfer from the front of the machine to the rear of the machine, which affects acceleration and the amount of the weight on the skis (which affects steerability).
In light of the varying characteristics that can be built into a suspension system, a variety of competing suspension systems have been made commercially available, and different types of suspension systems commonly are employed on different types of machines, depending upon their primary usage (e.g., racing, touring, etc.).